Known methods of producing erythritol include a method comprising cultivating a yeast strain belonging to the genus Trigonopsis or Candida in a culture medium containing glycerol as a carbon source and casein hydrolysate as a nitrogen source (Japanese Patent Publication No. 47-41549), and a method comprising cultivating a yeast strain belonging to the genus Candida, Torulopsis, or Hansenula in a culture medium containing hydrocarbons and the like as carbon sources and yeast extract and urea as nitrogen sources (Japanese Patent Publication No. 51-21072). These methods, however, have not yet been industrialized since raw materials used as carbon sources are not suitable for actual industrial production.
Alternatively, it is known to produce erythritol by cultivating Moniliella tomentosa var. pollinis in a culture medium containing carbohydrate such as glucose as carbon sources and corn steep liquor, urea, and yeast extract as nitrogen sources (Japanese Patent Laid Open No.60-110295 and the like) or by cultivating erythritol-producing microorganism in a culture medium containing yeast extract and corn steep liquor as nitrogen sources (Japanese Patent Laid-Open No. 1-199584).
Various substances are known as nitrogen sources as described above. However, urea is not admitted as food additives and therefore, it cannot be used for the production of erythritol which is applied to foods. On the other hand, yeast extract and casein hydrolysate is very expensive and therefore, they cannot be necessarily advantageous to industrial production. When corn steep liquor is used as a main nitrogen source, glycerol may be produced as a by-product, erythritol produced may be colored brown, or it contains a large quantity of salt. For these reasons, the purification process overloaded, which is disadvantageous to economical production.